1. Field of the Invention
This invention relates to hydrotreating of hydrocarbon feedstocks and more particularly to the catalytic treatment of petroleum and coal derived feedstocks to effect removal of sulfur and to reduce Conradson Carbon Residue (CCR).
2. Description of the Prior Art
The use of hydrotreating (HDT) to upgrade residual hydrocarbon fractions for use as charge stocks for catalytic cracking was well known in the art by the 1960's. Hydrotreating, as used herein encompasses those processes using hydrogen in the presence of catalysts in order to remove undesirable compounds from hydrocarbons, i.e., to upgrade the hydrocarbons.
By 1960, it was recognized that hydrotreatment of residues could be used for demetalation, dusulfurization, CCR reduction and denitrogenation. There was universal recognition at that time in the art that hydrogenation catalysts comprising Group VIA (Cr, Mo, W) and Group VIIIA metals or their oxides or sulfides deposited on porous refractory supports were extremely useful in hydrotreating processes. Preferred catalysts for hydrotreating were considered to be cobalt-molybdate or nickel-cobalt-molybdate supported on alumina. These catalysts are generally referred to in the art as "conventional HOT catalysts".
The use of zinc halide catalysts for the hydrocracking of polynuclear aromatics, such as coal extract, has been studied by the Research Division, Consolidated Coal Company, Library, Pennsylvania. The studies are described by Zielke et al in the following series of articles appearing in INDUSTRIAL AND ENGINEERING CHEMISTRY, PROCESS DESIGN AND DEVELOPMENT: Molten Zinc Halide Catalysts for Hydrocracking Coal Extract and Coal, Vol. 5, No. 2, April 1966, pages 158-164, and Fluidized Combustion Process for Regeneration of Spent Zinc Chloride Catalysts, Vol. 8, No. 4, October 1969, pages 552-558. In addition, Zielke et al also disclose the use of nickel-molybdate catalyst impregnated with 19% zinc chloride for hydrocracking, see INDUSTRIAL AND ENGINEERING CHEMISTRY, Vol. 5, No. 2 April 1966, pages 151-157.
U.S. Pat. No. 3,223,618 discloses a process for producing a high quality catalytic cracking feed stock comprising contacting an asphalt base crude oil contaminated with coke formers, sulfur, nitrogen and metals with zinc chloride. U.S. Pat. No. 3,677,932 discloses the use of a molten salt mixture comprising zinc halide and a modifying molten salt in a process for conversion of heavy petroleum fractions containing heteroatomic contaminants. Demetallization of hydrocarbons using zinc chloride and/or titanium tetrachloride is taught in U.S. Pat. No. 4,148,717.
Whereas a great amount of attention has been given to hydrotreating petroleum residual fractions, much less emphasis has been placed specifically on highly aromatic petroleum and coal derived liquids. In comparison with less aromatic hydrocarbon liquids, the desulfurization of highly aromatic liquids with conventional HDT catalysts is more difficult and has been less successful. Thus, U.S. Pat. No. 3,812,028 discloses a process for hydrotreating fossil fuels containing polynuclear aromatics utilizing a catalyst comprising activated carbon and a metallic component. U.S. Pat. No. 4,051,021 discloses a hydrodesulfurization process using a catalyst comprising a Group VI and/or Group VIII metal having a specified pore size distribution. In the process, a hydrocarbon feed is contacted with a conventional HDT catalyst having greater than 50 percent of its total pore volume of absolute diameter ranging from about 70 Angstroms to about 100 Angstroms.
The refining of synthetic crudes derived from sources such as coal, shale oil, tar sands and the like received consideration in papers delivered at the New Orleans Meeting of the Division of Petroleum Chemistry of the American Chemical Society held on March 20-25, 1977. The papers were published in the Society's Preprints, Vol. 22, No. 3, August 1977.
In comparison with conventional petroleum feedstocks, synthetically-derived hydrocarbons (e.g., coal liquids) and petroleum residua generally exhibit slightly higher carbon content, but significantly lower hydrogen content. Recent data suggests both a higher degree of aromaticity and a more highly condensed ring structure for coal liquids than for conventional petroleum type liquids.
A more striking difference between the synthetic hydrocarbons and conventional petroleum type liquids is the heteroatom content. Nitrogen, oxyen and sulfur levels in synthetic hydrocarbons are generally much higher than in petroleum. Furthermore, 40-70 wt. % of the nitrogen in coal liquids is basic in character as compared to 25-30 wt. % for typical conventional petroleum stocks. For these and other reasons, upgrading of aromatics-rich synthetic and petroleum derived hydrocarbons has not been as successful as that of conventional feedstocks having lower aromatics content.
Accordingly, it is a primary object of this invention to provide an improved process for hydrotreating hydrocarbon feedstocks.
It is an additional object of this invention to provide an improved process for hydrotreating of highly aromatic hydrocarbon feedstock.
It is yet another object of this invention to provide an improved hydrotreating catalyst.
Additional objects of this invention will become apparent to those skilled in the art from the study of the specification and the claims.